As an example of a vortex-flow blower device, there are known electric air pumps used in secondary air supply systems or the like. (Refer to JP-A-2005-69127 corresponding to US 2005/0047903 A1, for example.)
In the secondary air supply systems, when an engine has been just started and the temperature of its three way catalyst converter is low, air (secondary air), produced by operating an electric air pump, is guided to the three-way catalyst converter for purifying exhaust gas, and a three-way catalyst is thereby activated.
As illustrated in FIG. 5, a typical electric air pump used for secondary air supply systems includes: a resin impeller 101 having multiple fins 101a; a blower housing 104 having a vortex flow chamber 102 that covers the impeller 101 and a partitioning portion 103 that separates the discharge port side and the inlet port side of the vortex flow chamber 102 from each other; and an electric motor that rotationally drives the impeller 101.
When a driving relay for operation is turned on, the electric motor rotationally drives the impeller 101 in the electric air pump. When the impeller 101 is rotated, the air in the vortex flow chamber 102 is compressed from the vortex start point side to the vortex end point side by the movement of a large number of fins 101a. Since negative pressure is produced on the start point side of the vortex flow chamber 102, air is guided into the inlet port. Since high pressure is produced on the vortex end point side of the vortex flow chamber 102, pressurized secondary air is discharged from the discharge port and the discharged secondary air is guided into an exhaust pipe positioned upstream of the three way catalyst converter.
When the discharge side of the electric air pump is closed, the pressure in the blower housing 104 is raised, and the temperature in the blower housing 104 is raised. Even in this state, temperature rise can be suppressed within a normal temperature range for a predetermined control time, and thus any problem does not arise normally.
However, when the driving relay of the electric air pump is locked in on state, a harness for bypassing the driving relay is short-circuited, or any other like events for some unexpected reason are assumed as failure in the secondary air supply system, a problem arises. When the electric air pump operates for a time longer than a predetermined control time when the discharge side of the electric air pump is closed, the internal temperature of the blower housing 104 rises beyond the normal temperature range. As a result, the impeller 101 is thermally expanded by high-temperature air and the impeller 101 is brought into contact with the partitioning portion 103 of the blower housing 104. Then, the resin melted in the partitioning portion 103 gets caught in the impeller 101 and the impeller 101 is locked. As the result of the impeller 101 being locked, the impeller 101 may burst.
When the blower housing 104 is made of resin, the blower housing 104 can also be broken by the bursted impeller 101. Furthermore, when the blower housing 104 is broken, the broken blower housing 104 is supplied with the turning force of the impeller 101, and the broken pieces of the blower housing 104 may fly in all directions.